Ladar enabled impact mitigation system

ABSTRACT

A collision mitigation system is proposed which makes use of forward mounted long range ladar sensors and short range ladar sensors mounted in auxiliary lamps to identify obstacles and to predict unavoidable collisions therewith, and a duplex radio link in communication with secondary vehicles, and a number of external airbags deployable under the control of an airbag control unit, to reduce the forces of impact on the host vehicle, secondary vehicles, and bipeds and quadrupeds wandering into the roadway. A suspension modification system makes use of headlight mounted long range ladar sensors and short range ladar sensors mounted in auxiliary lamps to characterize the road surface, identify road hazards, and make adaptations to a number of active suspension components, each with the ability to absorb shock, elevate or lower the vehicle, and adjust the spring rate of the individual wheel suspensions.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/791,180filed on Mar. 8, 2013 entitled LADAR ENABLED IMPACT MITIGATION SYSTEMhaving a common assignee with the present application, the disclosure ofwhich is incorporated herein by reference.

BACKGROUND

1. Field

The embodiments disclosed herein relate generally to 3-D imagegeneration and the identification of objects, tracking of objects, roadhazard avoidance, and impact mitigation. Many systems have been proposedto meet the challenge of using optical imaging and video cameras in avehicle system to create 3-D maps of scenes and models of solid objects,and to use the 3-D database to navigate, steer, and avoid collisionswith stationary or moving objects. Stereo systems, holographic capturesystems, and those which acquire shape from motion, have all beenproposed and in some cases demonstrated, but what is lacking is a systemwith the capability of rapidly capturing 3-D images of objects androadway features in the path of a moving vehicle, or travelling on anintersecting path, and which controls and adapts the host vehicle so asto avoid collisions and road hazards, steer the best path, while at thesame time mitigating the impact and damage associated with anyunavoidable collisions.

2. References to Related Art

The 3-D imaging technology disclosed in Stettner et al, U.S. Pat. Nos.5,446,529, 6,133,989 and 6,414,746 provides with a single pulse oflight, typically pulsed laser light, all the information of aconventional 2-D picture along with the third dimensional coordinates;it furnishes the 3-D coordinates of everything in its field of view.This use is typically referred to as flash 3-D imaging in analogy withordinary digital 2-D cameras using flash attachments for a selfcontained source of light. As with ordinary 2-D digital cameras, thelight is focused by a lens on the focal plane of the LADAR sensor, whichcontains an array of pixels called a focal plane array (FPA). In thecase of a LADAR sensor these pixels are “smart” and can collect datawhich enables a processor to calculate the round-trip time of flight ofthe laser pulse to reflective features on the object of interest. Eachsmart pixel also collects data associated with the returning laser pulseshape and magnitude. One value of these flash LADAR sensors, as opposedto competing designs in which one or more pixels is scanned over thefield of view, is the elimination of the precision mechanical scanner,which is costly, high maintenance and typically large and heavy. Thepixels in the focal plane of a flash LADAR sensor are automaticallyregistered due to their permanent positions within the array. Further,by capturing a frame of data as opposed to one or a few pixels with onelaser pulse, the data rate is greatly increased while weight and volumeare reduced. Because each frame of data is captured from the reflectionof a short duration laser pulse, moving objects or surfaces ofstationary objects may be captured from a moving platform withoutblurring or distortion.

The driver and passengers of an automobile are exposed to dangers fromother vehicles and a number of road hazards. In some cases, a crash isunavoidable if the danger is presented suddenly, or the speed is toohigh to allow for a stop or an evasive maneuver. In these cases, it isimportant to lessen the damage caused by an impact, and to reduce theseverity of the impact. In other cases, where road hazards are present,or when sudden maneuver is imminent, adjustments to the suspension ofthe vehicle may improve ride and driver control, and may prevent damageto the vehicle tires, suspension, and undercarriage. To provide areference for acceleration levels during an automobile crash, a researchpaper is referenced, entitled “Finite Element Frontal Crash Analysis ofNEV Vehicle's Platform with Upper and Sub Frame Body”, by authors ByeongSam Kim, et. al., at the Department of Automotive Engineering, HoseoUniversity, Asan, Korea. In this research paper the authors perform acrash analysis of the upper body and sub frame for the NEV electric car.The NEV vehicle front platform assembly behavior when subjected to afrontal crash at 30 mph is described in this article which uses afinite-element analysis to model the behavior. One model of a variableor adjustable suspension is the Citroen® combined pneumatic andhydraulic vehicle suspension which is well documented in a number of webvideos, articles, and patents. An excellent multimedia web descriptionis at:http://www.citroenet.org.uk/miscellaneous/hydraulics/hydraulics-1.html,and a second is located at:http://www.kolumbus.fi/˜w496119/xw/technica5.htm. A detailed videodescription of the 2013 Citroen C5 Hydractive suspension may be foundat: http://www.youtube.com/watch?v=zuqJPurdRJw. A new type ofelectromagnetic suspension based on years of development by Bose islocated at:http://www.extremetech.com/extreme/97177-bose-active-suspension-moves-toward-market/2,and a video presentation may be viewed at:http://www.youtube.com/watch?v=Lyf4rfT7bHU&feature=related. Finally, acomparative discussion of active/semi-active suspensions may be foundat:http://www.autozine.org/technical_school/suspension/tech_suspension3.htm.These references together give a context for the present invention, andsupply background information on the operation of the adaptive andactive suspension systems being developed by the automobile industry.

SUMMARY OF THE INVENTION

Automobile occupants are exposed to dangers from other vehicles and roadhazards. A crash may be unavoidable if the danger is presented suddenly,or if speed is too high to allow for a stop or an evasive maneuver. Inthese cases, it is important to lessen the damage caused by an impact,and to reduce the severity of the impact. It is therefore desirable toprovide a system which uses a flash LADAR to generate 3D data describingobjects and obstacles in the path of the automobile, and a vehiclereaction capability to deploy airbags to mitigate the effects of impact,and to make adjustments to the vehicle suspension which may enhancedriver control, improve ride, and avoid damage to the tires, suspension,and undercarriage of the vehicle. If more than one vehicle is involvedin the imminent collision, radio or infrared communication may beestablished between the vehicles, and the steering and braking systemsof one or both of the cars may be activated to alter the impact from ahead-on collision to an oblique, or glancing impact, thus minimizing therate of energy dissipated in an impact. The prototypical system ismounted in a motor vehicle and may synthesize 3-D solid object modelsfrom data supplied by multiple ladar sensors and conventional 2D videocameras with overlapping fields of view.

The embodiments disclosed herein provide a system for crash mitigation,object and obstacle recognition and avoidance, and ride and steeringcontrol improvements. The benefits are realized through the use of a 3-Dimaging facility, comprising a vehicle mounted ladar system with anobject detection and recognition capability, an external airbagdeployment system, and a ride and suspension modification system. Thevehicle mounted ladar system may comprise a number of independent ladarsensors connected to a central ladar system controller which synthesizesthe available data from each of the independent ladar sensors into acomposite 3D map of the area in the path of the vehicle and in somecases, in a full 360 degree arc surrounding the vehicle. In a preferredembodiment, conventional 2D still images or video sequences may be usedto improve the quality of 3D solid models and scene maps. The multipleladar sensors each have an illuminating laser module which mayincorporate a semiconductor laser with a modulated laser light output,or a pulsed solid state laser, and a diffusing optic for illuminating ascene in the field of view of the modular ladar sensor. Each ladarsensor also comprises a receiver module featuring a two dimensionalarray of light sensitive detectors positioned at a focal plane of alight collecting and focusing assembly. The ladar sensor may beincorporated into a headlight, taillight, or other auxiliary lampassembly. The ladar sensor may also be part of a backup light, rearviewmirror assembly, or mounted behind an opening in a bumper or grillassembly. The individual ladar sensors rely on an array of lightsensitive detectors positioned at a focal plane of a light collectingand focusing assembly (Focal Plane Array or FPA). Each of the lightsensitive detectors has an output producing an electrical responsesignal from a reflected portion of the laser light output. Theelectrical response signals are connected to a readout integratedcircuit with a corresponding array of unit cell electrical circuits.Each of the unit cell electrical circuits has an input connected to oneof the light sensitive detector outputs, an electrical response signaldemodulator, and a range measuring circuit connected to an output of theelectrical response signal demodulator. The demodulator may be a voltagesampler and analog shift register for storing sequential samples of theelectrical response signals, or it may comprise a mixer, integrator, ormatched filter. The demodulation may also take place external to thereadout integrated circuit, by a fast digital processor operating on asequence of digitized samples from each pixel. The fast digitalprocessor may employ algorithms which utilize weighted sums ofsequential analog samples, or use fast Fourier transforms, convolution,integration, differentiation, curve fitting, or other digital processeson the digitized analog samples of the electrical response. The fastdigital processor may also employ algorithms which isolate or segmentthe roadway from other objects and objects from each other. Such objectsmay be automobiles, bicycles, motorcycles, trucks, persons, animals,walls, signs, road obstructions etc. These algorithms may computeposition and orientation, as well as object velocity. Objects, theirorientation, position and velocity may be transferred to a centralcomputer for further processing and decision making. The unit cell mayalso incorporate a trigger circuit, set to produce an output responsewhen the output of the demodulator exceeds a preset threshold. The rangemeasuring circuit is further connected to a reference signal providing azero range reference for the modulated laser light output. Theindividual ladar sensor may also incorporate a detector bias circuitconnected to a voltage distribution grid of the detector array and atemperature stabilized frequency reference. In some collision scenarios,both vehicles may be equipped with a radio link and may exchangeinformation including position, velocity, vehicle weight, system status,etc., and may cooperatively interact to reduce the impact of a collisionand lessen the destructive forces on the vehicles and occupants therein.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical collision threat scenario with a firstvehicle approaching a second vehicle which has spun out on the roadahead;

FIG. 2 is a diagram of an unavoidable collision in process wherein anexternal airbag deploys from a first vehicle to lessen the peak impactforces on a second vehicle;

FIG. 3 shows a second type of collision threat scenario with a vehicleapproaching a biped crossing a thoroughfare in the direct path of thevehicle;

FIG. 4 shows the evolution of FIG. 3, as a second type of unavoidablecollision wherein an external airbag deploys from a vehicle to lessenthe peak impact forces on a biped;

FIG. 5 shows a third type of collision threat scenario with a vehicleapproaching a quadruped crossing a thoroughfare in the direct path ofthe vehicle;

FIG. 6 shows a third type of unavoidable collision wherein an externalairbag deploys from a vehicle to lessen the peak impact forces on aquadruped.

FIG. 7 shows a diagram of an externally deployable airbag unit having aswitchable gas venting system, and suitable for mounting in a frontbumper area of an automobile;

FIG. 7A shows a partial cutaway view of the internal construction of anelectrically activated gas venting valve;

FIG. 8 is a partial cutaway view of a continuously variable gas ventingsystem using a slide and overlapping slots.

FIG. 9 is a chart with two acceleration curves, one curve for anunmitigated crash, and a second curve showing the effects of the impactmitigation system described herein;

FIG. 10 is a diagram of a double wishbone type motor vehicle suspensionassembly which features both passive and active road adaptingcapability, and with nominal ride height set by hydraulic pressure,pneumatic pressure, or by electromagnetic force;

FIG. 11 is a partial cutaway view of a double wishbone type motorvehicle suspension assembly which features both passive and active roadadapting capability and with nominal ride height set by a coil spring.

FIG. 12 is a diagram showing a motor vehicle equipped with ladar sensorsand an impact mitigation system of the present type, and several typesof common road hazards;

FIG. 13 is a diagram showing the passive adaption capability of themotor vehicle suspension of a preferred embodiment;

FIG. 14 is a diagram showing the active adaption capability of the motorvehicle suspension of a preferred embodiment;

FIG. 15 is a diagram showing a third scenario in which vehicle stabilityand traction may be enhanced by the active adaption capability of themotor vehicle suspension;

FIG. 16 is a block diagram showing the configuration of the ladarsystem, the individual ladar sensors, the host vehicle electrical andoptical systems, and the several subsystems of the host vehiclesupporting the impact mitigation system;

FIG. 17 is a block diagram showing additional details of the ladarsystem controller of FIG. 16, and the interconnection of the ladarsystem controller to the several ladar sensors installed on the vehicle;

FIG. 18 is a block diagram showing the configuration and components ofthe individual ladar sensors of FIGS. 16 & 17.

FIG. 19 is a schematic diagram showing the configuration and componentsof the unit cell electronics of the readout integrated circuit of FIG.18.

FIG. 20 is an isometric view of the hybrid assembly of the detectorarray and readout integrated circuit described in FIGS. 18 and 19.

DETAILED DESCRIPTION

This application contains new subject matter related to previous U.S.Pat. Nos. 5,696,577, 6,133,989, 5,629,524, 6,414,746, 6,362,482,D463,383, and U.S. patent application Ser. No. 10/066,340 filed on Jan.31, 2002 and published as US 2002/0117340 A1, the disclosures of whichare incorporated herein by reference.

The present invention is an impact mitigation system enabled by avehicle mounted ladar imaging system. The impact mitigation can be anairbag deployment, or a maneuver designed to reduce peak forces betweenvehicles, or to crash as safely as possible. The system may also adaptthe suspension of the vehicle so as to maintain traction on an irregularroad surface, or to avoid dangerous obstacles in the roadway. Each ladarimaging system typically consists of multiple vehicle mounted ladarsensors. Each ladar sensor may have a system control processor withfrequency reference and inertial reference, a system memory, a pulsedlaser transmitter, transmit optics, receive optics, an array of lightdetecting elements positioned at a focal plane of the receive optics, adetector bias converter for supplying bias voltage to the lightdetecting focal plane array, a readout integrated circuit,analog-to-digital converter circuits for producing digital image datafrom the analog readout IC outputs, a data reduction processor foradjusting and correcting the image data, and an object trackingprocessor for segregating, isolating, identifying, and tracking featuresand objects in the corrected image database. When paired with anintelligent vehicle system controller with external airbags systems andactive suspension controls, a substantial reduction in collision damage,and less frequent and severe damage to the undercarriage of the vehicleis expected. Each pixel in a focal plane array (FPA) of the preferredladar sensor converts impinging laser light into an electronic signalwhose magnitude is sampled in time and stored in memory within thepixel. Each pixel also uses a clock to time the samples being taken inresponse to the captured reflection of the laser light from a targetsurface. A preferred embodiment may include a two way radio/IR linkbetween vehicles, over which raw data, processed data, image data,object data, or commands may be shared as way of creating a cooperativeleast damage impact path for both vehicles. The ladar sensor typicallyincorporates a hybrid assembly of focal plane array and readoutintegrated circuit, and the readout IC is arranged as an array of unitcell electrical circuits, and each unit cell is arranged to be in anarray of identical spacing and order as the mating focal plane array.The ladar sensor in a preferred embodiment is capable of working in aflash mode as described above, or in a multi-pulse mode, or in a pulsedcontinuous-wave mode as the situation dictates. The impact mitigationsystem incorporating the ladar sensor has a number of features whichenable full 3D object modeling and tracking, as well as sceneenhancements derived from the merging of 2D and 3D data bases andmanaging of both 3D ladar sensors and conventional 2D video cameras.

FIG. 1 depicts a first embodiment of the impact mitigation systeminstalled on a first vehicle 2 involved in a collision threat scenariowith a second vehicle 8, which is spunout and stationary in the roadwayahead. The forward radiation pattern 6 of a long range ladar sensorembedded in a headlight assembly of first vehicle 2 is shown by dashedlines where it intersects with the driver's side of second vehicle 8,which is positioned laterally across the lane and the right edge of theroadway 9. Second vehicle 8 obstructs part of the second lane oftraffic, but does not extend over the left edge of the roadway 18. Asecond forward radiation pattern 7 from a second long range ladar sensorembedded in a second headlight assembly is shown overlapping firstradiation pattern 6. The radiation pattern 12 of a short range ladarsensor embedded in an auxiliary lamp assembly is shown projectingradially from a corner of first vehicle 2 and also at the other threecorners of first vehicle 2. First vehicle 2 also has a radio antenna 14for communicating with second vehicle 8 which also has a radio antenna16 for receiving radio communications and transmitting responses.Communication may also take the form of optical pulses.

FIG. 2 shows the evolution of FIG. 1 in a situation where first vehicle2 is unable to stop in time to avoid a collision with second vehicle 8.This scenario could easily evolve on a rain-slickened or icy roadway, orin the case of a second vehicle 8 emerging from a blind alleyperpendicular and to the right of the roadway edge 9. The headlightassembly 4 containing a long range ladar sensor is shown on firstvehicle 2. Also shown is the auxiliary lamp assembly 10 containing ashort range ladar sensor typically positioned at the four corners offirst vehicle 2. An external airbag 22 has been deployed from airbagpanel 20 mounted in the front bumper area of first vehicle 2. The firstvehicle 2 has determined an impact is likely from analyzing object datadeveloped from an array of available data, including long range andshort range ladar sensors, video/still cameras, GPS or relative positionreferences, and two way communications with second vehicle 8, and hasdeployed airbag 22 to reduce the closing speed between the vehicles inan unavoidable impact. It is also possible that second vehicle 8 bymeans of a side sensor could detect the danger and deploy an externalside air bag. The situation would be similar to FIG. 2.

FIG. 3 shows a collision threat scenario involving first vehicle 2 and abiped 24 in the roadway 18 ahead. Seen from a side view, first vehicle 2has a conical radiation pattern 6 emanating from a long range ladarsensor embedded in headlight assembly 4, for example, and whichilluminates biped 24 and returns range data sufficient to create a 3Dmodel. The 3D range data derived from the reflections of the modulatedlaser light allows for some object identification to take place in aprocessor of the impact mitigation system installed on first vehicle 2.Short range radiation pattern 12 issues from a short range ladar sensorwhich is embedded in auxiliary lamp assembly 10, and covers the groundimmediately in front of first vehicle 2. Auxiliary lamp assembly 10 inthis diagram is embedded in a corner mounted turn signal, as depicted inFIG. 1. An airbag system is contained in airbag panel 20 located in thefront bumper of first vehicle 2.

FIG. 4 shows a side view of the moment of impact between first vehicle 2and biped 24. Airbag 22 is fully deployed and ready to absorb the impactto reduce damage to the vehicle 2 and to soften the blow delivered tobiped 24. Front wheel 21 may actively lower to prevent the possibilityof first vehicle 2 knocking biped 24 over and running over it ordragging it. Rear wheel 17 may lower as well, or may remain in position.Also shown is auxiliary lamp assembly 10, a tail light in this case,which may have a short range ladar sensor embedded. Ladar sensors may bemounted at many points on the vehicle 2; door panels, rear view mirrors,bumpers, etc. Rear bumper 26 and door panels 19 may also have externalairbag systems as well which may be activated in the event of a rear orside impact to first vehicle 2.

FIG. 5 shows a collision threat scenario involving first vehicle 2 and aquadruped 28 in the roadway 18 ahead. Seen from a side view, firstvehicle 2 has a conical radiation pattern 6 emanating from a long rangeladar sensor embedded in headlight assembly 4, and which illuminatesquadruped 28 and returns range data sufficient to create a 3D model. The3D range data derived from the reflections of the modulated laser lightallows for some object identification to take place in a processor ofthe impact mitigation system installed on first vehicle 2. Short rangeradiation pattern 12 issues from a short range ladar sensor which isembedded in auxiliary lamp assembly 10, and covers the groundimmediately in front of first vehicle 2. Auxiliary lamp assembly 10 inthis diagram is a corner mounted turn signal. An airbag system iscontained in airbag panel 20 located in the front bumper of firstvehicle 2.

FIG. 6 at far right shows a side view of the moment just after impactbetween first vehicle 2 and quadruped 28 has been upended and isrotating. Airbag 22 is fully deployed and has been deployed in a mannerto ensure quadruped 28 is not run over and dragged by first vehicle 2.The external airbag 22 has been fully vented to minimize the impact onquadruped 28. Front wheel 21 suspension may actively compress and lowerthe front of vehicle 2, so as to prevent the possibility of vehicle 2knocking quadruped 28 over and running over it or dragging it. Alsoshown is auxiliary lamp assembly 10, a taillight in this case, which mayhave a short range ladar sensor embedded. First vehicle 2 travelsforward in the direction of arrow 30. At the left of FIG. 6, thecollision has evolved a bit further, with the quadruped 28 fully rotatedinto a back-down position, resting on the hood of vehicle 2 withoutcrushing antenna 14.

FIG. 7 shows an isometric view of an airbag panel 20 with an externalairbag 22 compacted and stored thereon, and having a series of remotelyactuated solenoid valves 23 mounted thereto. Each of the solenoid valves23 has a switchable air passageway with an exit aperture 25 andelectrical connections 27. In the case of a full frontal collision witha second vehicle 8, the air passageways would be closed, and maximumenergy absorption is the result. In the case of a collision with a biped24 or quadruped 28, the valves may be opened by the first vehicle 2 oncethe onboard computer processors recognize the type of object which islikely to be impacted. To adjust the gas flow resistance of the externalairbag 22, 1, 2, or 3 valves may be opened, depending on the size anddensity characteristic of the identified object. FIG. 7A is a partialcutaway of a solenoid valve 23 showing the internal working elements.The overall shape is a cylindrical plug which may be mounted to panel 20by screwing threaded section 45 into airbag panel 20 until shoulder 47stops the advance. An air or gas passageway inlet 29 communicates withan exit air or gas passageway 25 interrupted by clapper valve 31 whichrotates on pivot 37. A fail-safe spring 43 forces the clapper valve 31shut when electrical power is lost, or when solenoid 39 is stuck ornon-operational. Valve seats 35 are machined to mate with the taperedsection 33 of clapper 31. A solenoid type magnetic actuator 39 with alinear moving plunger 41 opens the clapper valve 31 when an electriccurrent is applied through electrical connections 27.

FIG. 8 is another embodiment of a gas venting system for the externalairbag 22. Airbag panel 20 is configured with a series of slots 53 whichmay be covered by solid sections of sliding plate 49, or opened to apartially open position when the slots 51 and 53 are partiallyoverlapping. A maximum gas venting aperture is created by the fully openposition when the slots 51 of sliding plate 49 are directly atop theslots 53 of airbag panel 20. A U-shaped channel 59 at the bottom ofairbag panel 20 guides sliding plate 49, and holds it in position to actas a variable gas valve for venting external airbag 22 after deployment.A second U-shaped channel (not shown) at the top of airbag panel 20retains and guides sliding plate 49, and retains it in position to beeffective as a variable aperture gas valve. A mechanical stop 61 keepssliding plate 49 from traversing beyond the fully closed position. Aspring force 55 from a failsafe spring (not shown) keeps sliding plate49 pressed against mechanical stop 61 in normal operation, and the ventsfully closed. In the event of an anticipated collision with a biped 24or quadruped 28, a linear force 57 from a linear actuator such as anelectromagnetic solenoid (not shown), moves the sliding plate 49 open tothe degree selected by the onboard airbag control unit. The ability tovent the external airbag 22 with a continuously variable exit apertureformed by a plurality of overlapping slots 51 and 53 gives the airbagcontrol unit a degree of freedom necessary to prevent injury to bipeds24 and quadrupeds 28 appearing suddenly in the roadway, whilemaintaining the maximum airbag force for other vehicle-only typecollisions.

The operations of the external airbag system are conceptually simple; acentral airbag control unit (ACU) monitors the ladar sensors and anumber of other sensors within the vehicle 2, including accelerometers,impact sensors, side (door) pressure sensors, wheel speed sensors,gyroscopes, brake pressure sensors, and seat occupancy sensors. When therequisite threshold conditions have been reached or exceeded, the airbagcontrol unit will trigger the ignition of a gas generator propellant torapidly inflate the airbag envelope. As the vehicle 2 collides withanother vehicle or obstacle and compresses the bag, the gas escapes in acontrolled manner through venting holes. The airbag volume and the sizeof the vents may be tailored to each vehicle 2, to spread out thedeceleration of the vehicle 2, and thereby limit the forces of impact onthe vehicle 2. The signals from the various sensors are fed into theairbag control unit (118 in FIG. 16), which determines from them theprojected angle of impact, the severity, or force of the crash, andother variables. Depending on the result of these calculations, the ACU118 may also deploy internal occupant restraint devices, such as seatbelt pre-tensioners, internal airbags (including front internal airbagsfor driver and front passenger, along with seat-mounted side internalairbags, and “curtain” airbags which cover the side glass). Eachexternal airbag 22 as well as internal occupant restraint device istypically activated with one or more pyrotechnic devices, commonlycalled an initiator or electric match. The electric match, whichconsists of an electrical conductor wrapped in a combustible material,activates with a current pulse between 1 to 3 amperes in less than 2milliseconds. When the conductor becomes hot enough, it ignites thecombustible material, which initiates the gas generator. In an airbag,the initiator is used to ignite solid propellant inside the airbaginflator. The burning propellant generates inert gas which may inflatean external airbag 22 in approximately 30 to 50 milliseconds. Anexternal airbag 22 must inflate quickly in order to be fully inflated bythe time the forward-traveling vehicle 2 reaches the impact zone. Thedecision to deploy an external airbag 22 in a frontal impact must bemade 60-80 milliseconds prior to the anticipated time of the crash, sothe front bumper mounted external airbag(s) 22 may be fully inflatedprior to the first moment of vehicle contact.

FIG. 9 is an acceleration diagram of forces transmitted through thesub-frame and upper frame of a typical motor vehicle in a simulatedcrash. The results of the simulation are plotted as acceleration curve32 in solid black lines, showing acceleration peaks in excess of 12Gs(12 times the force of gravity, G=9.8 m/s²). With the deployment of anexternal airbag, the expected acceleration is plotted as dotted line 34,which initiates earlier and shows acceleration peaks of approximately8Gs. The effect of the external airbag 22 deployment in a frontal crashis expected to be the reduction in severity of the impact as can be seenin the projected acceleration curve 34 as opposed to the originalsimulated acceleration 32.

FIG. 10 is a diagram of a suspension type common to many contemporarymotor vehicles, the so-called double wishbone suspension. In thissuspension type, two rigid A-arms, an upper A-arm 56, and a lower A-arm46, support an upright 68 which carries the hub and wheel 36. The upperA-arm 56 and lower A-arm 46 are both in the shape of a wishbone, withthe open end of lower A-arm 46 having a cylindrical pivot end 48rotating about the axis of shaft 50 which attaches through the frame ofthe vehicle. Upper A-arm 56 also has a cylindrical pivot end 58 rotatingabout a second shaft 50 connected through the frame of the vehicle. Thefar end of the second shaft then connects to the other open end of theupper A-arm 56. The outer end of upper A-arm 56 connects to upright 68through a pivot bearing 66. The outer end 42 of lower A-arm 46 connectsto a lateral projection 40 of upright 68 through a pivot bearing 38. Anactive suspension component 61 comprising a cylinder 54 and piston 52connects to lower A-arm 46 at pivot joint 44 and to the frame of thevehicle at pivot joint 64. The active suspension component 61 connectsto the vehicle frame at pivot joint 64 by passing through the open endof upper A-arm 56. A fitting 62 and umbilical 60 connect to the vehiclecontrol systems. Fitting 62 may be hydraulic, pneumatic, or electrical,and may connect to the vehicle hydraulic, pneumatic, or electricalsystems, or in some embodiments to any two, or all three systems.Umbilical 60 may be an air hose, hydraulic fluid line, electricalconnecting wires, or may comprise any two, or all three types ofconnections. None of the steering linkages are shown in the diagram ofFIG. 10 for the sake of clarity. This suspension system relies onhydraulic fluid and pneumatic pressure to set the nominal ride height asin the Citroen Hydractive® suspension system. An electromagnetic linearactuator with a coil and stator housed in the body of cylinder 54 mayact as an active damper. The electromagnetic linear actuator operates ina manner similar to the Bose® electromagnetic suspension described inthe references and is capable of modifying the ride height, absorbingshock and converting the energy of the shock to electrical energy, andelevating the vehicle dynamically if required.

FIG. 11 shows a second embodiment of a variable ride suspension systemwith a coil spring 70 providing the nominal ride height for the vehicle.Coil spring 70 mounts coaxially over the outside diameter of cylinder 54of active suspension component 61. The tire 78, rim 76, and wheel 74 arepartially cut away to give a better view of the upright 68 and hub 72.Lower spring cup 75 is rigidly attached to piston 52 of activesuspension component 61 and engages with the bottom end of coil spring70. Upper spring cup 73 engages with the top of coil spring 70 and restssecurely against the fender (not shown) of the vehicle indicated bydashed line 77. Fitting 62 is repositioned to be accessible through thefender of the vehicle, and umbilical 60 connects to the vehicleelectrical, pneumatic, and/or hydraulic systems. FIG. 11 does not showany of the vehicle steering linkages in the interests of clarity.

FIG. 12 shows a road hazard scenario involving first vehicle 2 and a dip82 in the roadway 18, a pothole 84 with an abrupt edge, and the sideprofile 80 of a 4″×4″ stick of lumber 86 which has fallen off the backof a truck. Seen from a side view, first vehicle 2 has a conicalradiation pattern 6 emanating from a long range ladar sensor embedded inheadlight assembly 4 and which illuminates the 4×4 in the distance andreturns range data sufficient to create a 3D model. The 3D range dataderived from the reflections of the modulated laser light allows forsome object identification to take place in a processor of the impactmitigation system installed on first vehicle 2. Short range radiationpattern 12 issues from a short range ladar sensor which is embedded inauxiliary lamp assembly (10 in FIG. 13) and covers the groundimmediately in front of first vehicle 2. The auxiliary lamp assembly (10in FIG. 13) in this diagram is a corner mounted turn signal, though theladar sensor may be mounted in several other points on the vehicle. Thedip 82 in the roadway 18 has been swept out by the long range ladarsensor and previously identified. Dip 82 is swept out a second time by ashort range ladar sensor with a wider angle of divergence, and adecision is made by the navigation and suspension processor onboardfirst vehicle 2, which typically runs autonomously, and which may adaptthe suspension continuously. The decision is made to adapt the vehiclesuspension to maintain contact with the roadway and maintain maximumcontrol of the vehicle 2, and the result is shown graphically in FIG.13.

In FIG. 13, the onboard suspension control system, knowing the depth andshape of the dip 82, and the spring rate of the coil spring orcompressed air bearing the vehicle load, may simply allow the suspensionto passively track through the dip 82. For some types of dips 82, andsome suspension characteristics, this may be an optimum solution for thestability and control of the vehicle 2. In the case of a deep dip 82, ora soft sprung vehicle suspension, it may be necessary to actively drivethe left front wheel 21 lower by using an electrical impulse into anactive suspension component 61 as described in association with FIGS. 10& 11. In an alternative embodiment, hydraulic fluid under pressure maybe applied to active suspension component 61, and used to drive the leftfront wheel 21 lower into the dip 82. In a third embodiment, an impulseof compressed air is applied to an active suspension component 61 inorder to drive the left front wheel 21 lower into the dip 82 in order tomaintain maximum traction and road contact. Further down the road, apothole 84 with an abrupt edge dictates a different reaction from theactive suspension system, and in the distance, 4×4 80 requires analtogether different reaction.

At the center of FIG. 14 is a side view of vehicle 2 traversing aparticularly dangerous pothole 84 having an abrupt edge at the terminus.A typical passive suspension would track front wheel 21 down into thedepth of the pothole 84 and then violently impact the abrupt terminaledge of the pothole 84. Rear wheel 17 also has an active suspensioncomponent 61 which has tracked through the dip 82 and is shown in thediagram still partially extended as vehicle 2 exits the dip 82. Pothole84 has been profiled in 3D by both a long range ladar sensor embedded inheadlight 10 and by a short range ladar sensor embedded in auxliary lamp10, and is therefore well characterized, and a decision has been made toglide over the pothole 84 on a planar path 88, and thus front wheel 21has been actively restrained from tracking down into the depression ofpothole 84, and in some cases, might be partially retracted to avoidcontact with the abrupt edge of pothole 84. The front wheel 21 may beactively restrained from descending by an active suspension component 61in the suspension of the left front wheel 21 of vehicle 2. At the farleft of FIG. 14, vehicle 2 is negotiating a safe path over 4×4 80, byrapidly driving front wheel 21 downward at a high enough rate to elevatethe front end of vehicle 2 sufficient to clear the obstacle representedby the 4×4 80. Once the front end of vehicle 2 is slightly airborne, thefront wheel 21 may be retracted upward actively by the same activesuspension component 61 which is used to elevate the front end ofvehicle 2, allowing front wheel 21 to clear an obstacle with a heightgreater than the vertical elevation of the front end of vehicle 2. Asimilar regimen may be employed using an active suspension component 61in the suspension of rear wheel 17 to elevate the rear end of vehicle 2as it encounters the obstacle represented by 4×4 80. In some cases,where the speed of the vehicle and the conditions allow, the suspensionmay even be actively compressed prior to initiation of a downward thrustfrom active suspension component 61, allowing for a full travel of theactive suspension component 61, and therefore greater vertical elevationof the front end of vehicle 2. All of these vertical maneuvers describedin FIGS. 12-14 assume there are not better, or less disruptive maneuversrelying solely on steering and/or braking to avoid or contain the damagefrom road hazards, and would typically be used as a secondary option inthe event a simple lane change would not be a viable solution. Avoidingdamage from road hazards can be key to avoiding damage to the chassisand undercarriage of the vehicle 2, and to avoiding accidents caused bya loss of control of the vehicle 2 such as might be expected from ablown out tire, shattered suspension, or loss of steering.

FIG. 15 shows another scenario requiring a slightly different type ofsuspension adjustment. Entering a banked curve (9, 18) at high speed,vehicle 2 needs to adjust the right side (outside of the curve 9)suspension to be stiffer, i.e., a higher spring rate, and may need toalso lower the driver (left) side of the car. These actions may preventthe car from diving lower into the outside of the curve 9, and thus keepthe weight distribution on the four wheels evenly divided. This can becompleted autonomously by the vehicle 2 using the present activesuspension components 61 attached to each wheel. On the right side ofvehicle 2, a reduction in air volume may effect an increase in springrate in a manner similar to the reaction of the Citroen® suspensionsystem. If the active suspension component 61 is a solenoid, additionalinductance may give a higher spring rate. Additional inductance may beprovided for by electrically switching in coils which have beenpre-wound but not connected electrically. However, the preferred methodis to use a dynamic electrical controller which can give a stiffer rideby reacting more forcefully to each deflection of the wheel 36 andcontrol arms 46, 56 by applying increasing amounts of current to thesolenoid in opposition to the natural movement of the wheel 36. Anelectrical impulse, or a step in gas pressure, or a change in thepressure of a hydraulic fluid may be used to lower the left side of thevehicle 2 relative to the right side in a left hand turn. At high speed,or when the curve is banked, the calculation of the amount of loweringmay be adjusted by an onboard processor. The slope of the curve 92 isshown in the cross section of dashed line AA, and the slope, or bank hasbeen fully mapped out by the radiation pattern 6 of the long range ladarsensors embedded in each of the steerable headlights 4. Unlike theexample of the Citroen® suspension, which adapts the vehicle suspensionreactively to reduce roll, the ladar enabled suspension modifyingcapability of the present invention allows the suspension to be adjustedproactively, in advance of the need, because of the 3D roadway sensingand modelling capabilities.

FIG. 16 is a block diagram of a preferred embodiment of the ladarenabled impact mitigation system. A ladar system controller 104communicates with all 6 of the ladar sensors mounted on the vehicle. Ina typical installation, two long range units, LRU 1 94 and LRU 2 96connect to ladar system controller 104 through a set of bidirectionalelectrical connections 98. The electrical connections 98 may also havean optical waveguide and optical transmitters and receivers to transferdata, control, and status signals bidirectionally between long rangeladar sensors 94 and 96 to ladar system controller 104. Ladar systemcontroller 104 also communicates with the 4 short range units, SRU 1102, SRU 2 100, SRU3 106, and SRU4 108, each through a set ofbidirectional electrical connections 110. The electrical connections 110may also have an optical waveguide and optical transmitters andreceivers to transfer data, control, and status signals bidirectionallybetween short range ladar sensors 102, 100, 106, and 108, to ladarsystem controller 104. Each of the ladar sensor's ladars may includedata processors to reduce the processing load on the central processor;for example, developing the point cloud and isolating/segmenting objectsin the field of view and object speed from the point cloud. A number (n)of conventional 2D still or video cameras 97 also connect to ladarsystem controller 104, and are designed to overlap the fields of view ofthe ladar sensors installed on the vehicle 2. Bidirectional electricalconnections 112 serve to transfer 3D data maps, status, and controlsignals between ladar system controller 104 and the vehicle electricalsystems and central processing unit (CPU) 114. At the core of thevehicle, an electronic brain may control all functioning of the vehicle2, and typically controls all other subsystems and co-processors. Theelectronic brain, or central processing unit (CPU 114) is here lumpedtogether with the basic electrical systems of the vehicle, includingbattery, headlights, wiring harness, etc. The vehicle suspension system116 receives control commands and returns status through bidirectionalelectrical connections, and is capable of modifying the ride height,spring rate, and damping rate of each of the four wheels independently.An inertial reference 120 also has a vertical reference, or gravitysensor as an input to the CPU 114. A global positioning reference 122may also be connected to the vehicle CPU 114. The GPS reference 122 mayalso have a database of all available roads and conditions in the areawhich may be updated periodically through a wireless link A duplex radiolink 115 may also be connected to CPU 114, and communicate with othervehicles 8 in close range and which may be involved in a future impact,and may also receive road data, weather conditions, and otherinformation important to the operations of the vehicle 2 from a centralroad conditions database. The vehicle 2 may also provide updates to thecentral road conditions database via radio uplink 115, allowing thecentral road conditions database to be augmented by any and all vehicles2 which are equipped with ladar sensors and a radio link 115. Acollision processor and airbag control unit 118 connects bidirectionallyto CPU 114 as well, receiving inputs from a number of accelerometers,brake sensors, wheel rotational sensors, ladar sensors, etc. and makesdecisions on the timing and deployment of both internal and externalairbags 22. ACU 118 also controls the venting of external airbags 22through bidirectional electrical connections to a number of ventcontrols 99 situated in the various external airbag units on the vehicle2.

FIG. 17. shows additional details of the ladar system controller 104 andinterconnections to the suite of ladar sensors. The ladar systemcontroller 104 comprises a sensor interface 126, which transmitscommands to the short range ladar sensors SRU1-4 (100, 102, 106, and108), and to the long range ladar sensors LRU1 94, and LRU2 96. A fibercable and wire harness 124 provides the physical media for the transferof the commands from the sensor interface 126 to the various ladarsensors. 3D data and status signals are returned from the various ladarsensors to sensor interface 126 through fiber cable and wire harness124. Likewise, command signals are sent to a number (n) of 2D cameras97, and status and image data are returned therefrom, via wire harness124 to ladar system controller 104. Each long range sensor unit (94, 96)connects through a set of bidirectional connections 98 which logicallyinclude the transmitters and receivers within each long range sensorunit (94, 96), the physical media of fiber cable and wire harness 124,and the transmitters and receivers of sensor interface 126. Each shortrange sensor unit (100,102,106,108) connects through a set ofbidirectional connections 110 which logically include the transmittersand receivers within each short range sensor unit (100,102,106,108), thephysical media of fiber cable and wire harness 124, and the transmittersand receivers of sensor interface 126. Sensor interface 126 receivesdigital logic levels from scene processor 128 and control processor 132and conditions these signals for transmission over fiber cable and wireharness 124 to the various ladar sensors installed on the vehicle 2.Sensor interface 126 may provide amplification, level adjustment,digital-to-analog conversion, and electrical-to-optical signalconversion for outbound signals from control processor 132 and sceneprocessor 128 intended for one or more of the various ladar sensors or2D cameras installed on the vehicle 2. Conversely, for inbound signals,sensor interface 126 may provide amplification, level shifting,analog-to-digital conversion, and optical-to-electrical conversion for3D or 2D data and status signals sent from any one of the various ladarsensors or 2D cameras installed on the vehicle 2 and then provides thesereceived and/or converted signals to control processor 132 and sceneprocessor 128 as digital signals. Scene processor 128 combines the 3Dframes received from each of the operational ladar sensors into acomposite 3D map of the entire space directly in front of andsurrounding the vehicle 2 and may also merge the 3D map with 2D imagedata received from a number (n) of 2D still or video cameras 97 toprovide enhanced resolution or object identification. Complete 3D mapsof the area surrounding the vehicle 2 are best enabled when theauxiliary, short range sensors are installed. In a preferred embodiment,the six ladar sensors comprised of 2 long range sensors and 4 shortrange sensors provide a full 360° field of view, and a 3D map may besynthesized by scene processor 128 for the entire space surrounding andin front of, vehicle 2. Overlapping fields of view between long rangesensors may allow scene processor 128 to eliminate some shadows in thefar field pattern, or to gain additional shape data which may allowpositive identification of an object or obstacle in the path of thevehicle 2. Overlapping fields of view between short range and long rangesensors give scene processor 128 additional shape information on anyfeature or object in the combined field of view, as well as a reductionof shadows, owing to the wider angles swept out by the short rangesensors. Control processor 132 receives status data from the ladarsensors indicating laser temperature, transmitted laser pulse power andpulse shape, receiver temperature, background light levels, etc. andmakes decisions about adjustments of global input parameters to thevarious ladar sensors being controlled. Global settings for detectorbias, trigger sensitivity, trigger mode or SULAR mode, filter bandwidth,etc. may be sent from control processor 132 to a given ladar sensorwhich may override the local settings originally set or adjusted by alocal control processor residing within a particular ladar sensor. Anon-volatile memory 130 provides a storage location for the programswhich run on control processor 132 and scene processor 128, and may beused to store status data and other data useful at start-up of thesystem. A data communications port 134 typically comprises an Ethernetport or Gigabit Ethernet port, but may be a USB, IEEE1394, Infiniband,or other general purpose data port, and is connected so as to providebidirectional communications between the control processor 132 or thescene processor 128 and the vehicle electrical systems and centralprocessors 114 through connections 112. Data communications port 134 mayalso be a special purpose communications port specific to a vehiclemanufacturer.

FIG. 18. is a block diagram a ladar sensor which describes both longrange ladar sensors 94 and short range sensors 100 typical of thepreferred embodiment. Adaptations of the pulsed laser transmitter 146,transmit optics 150, receive optics 152, and in some cases, programmablechanges to the sampling circuitry of readout integrated circuit 156 maybe effected to provide range enhancement, wider or narrower field ofview, and reduced size and cost. The first embodiment provides a 128×128detector array 154 of light detecting elements situated on a singleinsulating sapphire substrate which is stacked atop a readout integratedcircuit 156 using a hybrid assembly method. In other embodiments of thedesign, M×N focal plane arrays of light detecting elements with M and Nhaving values from 2 to 1024 and greater are anticipated. The functionalelements depicted in FIG. 18 may first be described with respect to theelements of a typical long range ladar sensor 94. A control processor136 controls the functions of the major components of the ladar sensor94. Control processor 136 connects to pulsed laser transmitter 146through bidirectional electrical connections (with logic, analog todigital (A/D) and digital to analog (D/A) converters 144) which transfercommands from system controller 136 to pulsed laser transmitter 146 andreturn monitoring signals from pulsed laser transmitter 146 to thesystem controller 136. A light sensitive diode detector (Flash Detector)148 is placed at the back facet of the laser so as to intercept aportion of the laser light pulse produced by the pulsed lasertransmitter 146. An optical sample of the outbound laser pulse takenfrom the front facet of pulsed laser transmitter 146 is routed to acorner of the detector array 154 as an automatic range correction (ARC)signal, typically over a fiber optic cable. The pulsed laser transmitter146 may be a solid-state laser, monoblock laser, semiconductor laser,fiber laser, or an array of semiconductor lasers. It may also employmore than one individual laser to increase the data rate. In a preferredembodiment, pulsed laser transmitter 146 is an array of vertical cavitysurface emitting lasers (VCSELs). In an alternative embodiment, pulsedlaser transmitter 146 is a disc shaped solid state laser of erbium dopedphosphate glass pumped by 976 nanometer semiconductor laser light.

In operation, the control processor 136 initiates a laser illuminatingpulse by sending a logic command or modulation signal to pulsed lasertransmitter 146, which responds by transmitting an intense pulse oflaser light through transmit optics 150. In the case of a solid statelaser based on erbium glass, neodymium-YAG, or other solid-state gainmedium, a simple bi-level logic command may start the pump laser diodesemitting into the gain medium for a period of time which will eventuallyresult in a single flash of the pulsed laser transmitter 146. In thecase of a semiconductor laser which is electronically pumped, and may bemodulated instantaneously by modulation of the current signal injectedinto the laser diode, a modulation signal of a more general nature ispossible, and may be used with major beneficial effect. The modulationsignal may be a flat-topped square or trapezoidal pulse, or a Gaussianpulse, or a sequence of pulses. The modulation signal may also be asinewave, gated or pulsed sinewave, chirped sinewave, or a frequencymodulated sinewave, or an amplitude modulated sinewave, or a pulse widthmodulated series of pulses. The modulation signal is typically stored inon-chip memory 142 as a lookup table of digital memory wordsrepresentative of analog values, which lookup table is read out insequence by control processor 136 and converted to analog values by anonboard digital-to-analog (D/A) converter 144, and passed to the pulsedlaser transmitter 146 driver circuit. The combination of a lookup tablestored in memory 142 and a D/A converter, along with the necessary logiccircuits, clocks, and timers 140 resident on control processor 136,together comprise an arbitrary waveform generator (AWG) circuit block.The AWG circuit block may alternatively be embedded within a laserdriver as a part of pulsed laser transmitter 146. Transmit optics 150diffuses the high intensity spot produced by pulsed laser transmitter146 substantially uniformly over the desired field of view to be imagedby the long range ladar sensor 94. An optical sample of the transmittedlaser pulse (termed an ARC signal) is also sent to the detector array154 via optical fiber. A few pixels in a corner of detector array 154are illuminated with the ARC (Automatic Range Correction) signal, whichestablishes a zero time reference for the timing circuits in the readoutintegrated circuit (ROIC) 156. Each unit cell of the readout integratedcircuit 156 has an associated timing circuit which is started countingby an electrical pulse derived from the ARC signal. Alternatively, theflash detector 148 signal may be used as a zero reference in a secondtiming mode. Though the ARC signal neatly removes some of the variabledelays associated with transit time through the detector array 154,additional cost and complexity is the result. Given digitalrepresentations of the image frames, the same task may be handled insoftware/firmware by a capable embedded processor such as data reductionprocessor 164. When some portion of the transmitted laser pulse isreflected from a feature in the scene in the field of view of the longrange ladar sensor 94, it may be incident upon receive optics 152,typically comprising the lens of a headlight assembly, a parabolicreflecting lens within the headlight assembly, and an array ofmicrolenses atop detector array 154. Alternative embodiments useenhanced detectors which may not require the use of microlenses. Pulsedlaser light reflected from a feature in the scene in the field of viewof receive optics 152 is collected and focused onto an individualdetector element of the detector array 154. This reflected laser lightoptical signal is then detected by the affected detector element andconverted into an electrical current pulse which is then amplified by anassociated unit cell electrical circuit of the readout integratedcircuit 156, and the time of flight measured. Thus, the range to eachreflective feature in the scene in the field of view is measurable bythe long range ladar sensor 94. The detector array 154 and readoutintegrated circuit 156 may be an M×N or N×N sized array. Transmit optics150 consisting of a spherical lens, cylindrical lens, holographicdiffuser, diffractive grating array, or microlens array, condition theoutput beam of the pulsed laser transmitter 146 into a proper conical,elliptical, or rectangular shaped beam for illuminating a centralsection of a scene or objects in the path of vehicle 2, as illustratedin FIG. 1.

Continuing with FIG. 18, receive optics 152 may be a convex lens,spherical lens, cylindrical lens or diffractive grating array. Receiveoptics 152 collect the light reflected from the scene and focus thecollected light on the detector array 154. In a preferred embodiment,detector array 154 is formed in a thin film of gallium arsenidedeposited epitaxially atop an indium phosphide semiconducting substrate.Typically, detector array 154 would have a set of cathode contactsexposed to the light and a set of anode contacts electrically connectedto the supporting readout integrated circuit 156 through a number ofindium bumps deposited on the detector array 154. The cathode contactsof the individual detectors of detector array 154 would then beconnected to a high voltage detector bias grid on the illuminated sideof the array. Each anode contact of the detector elements of detectorarray 154 is thus independently connected to an input of a unit cellelectronic circuit of readout integrated circuit 156. This traditionalhybrid assembly of detector array 154 and readout integrated circuit 156may still be used, but new technology may reduce inter-element coupling,or crosstalk, and reduce leakage (dark) current and improve efficiencyof the individual detector elements of detector array 154. In apreferred embodiment, the elements of detector array 154 may be formedatop a substantially monocrystalline sapphire wafer. Sapphire substrateswith a thin layer of substantially monocrystalline silicon are availablein the marketplace (SOS wafers), and are well known for their superiorperformance characteristics. A detector array 154 of APD, PIN, or PNjunction detectors may be formed of a sequence of layers of p-type andn-type silicon via epitaxial regrowth on the SOS wafers. Boron andaluminum may be used as dopants for any of the p-type silicon epitaxiallayers. Phosphorus, arsenic, and antimony may be used as dopants for anyof the n-type silicon epitaxial layers. Sapphire substrates with a thinlayer of substantially monocrystalline gallium nitride are alsoavailable in the marketplace (GNOS wafers), and are well known assubstrates well suited to the fabrication of high brightness blue LEDs.A detector array 154 of APD, PIN, or PN junction detectors may be formedof a sequence of layers of p-type and n-type gallium nitride (GaN) orindium gallium nitride (InGaN) via epitaxial regrowth on the GNOSwafers. Silicon and germanium may be used as dopants for any of then-type GaN layers. In some cases, magnesium may be used as a dopant forof the p-type layers in GaN. In a further development, detector array154 may be fabricated monolithically directly atop readout IC 156.Detector array 154 may also be formed in a more conventional manner fromcompounds of indium gallium arsenide, indium aluminum arsenide, siliconcarbide, diamond, mercury cadmium telluride, zinc selenide, or otherwell known semiconductor detector system. Readout integrated circuit 156comprises a rectangular array of unit cell electrical circuits, eachunit cell with the capability of amplifying a low level photocurrentreceived from an optoelectronic detector element of detector array 154,sampling the amplifier output, and detecting the presence of anelectrical pulse in the unit cell amplifier output associated with alight pulse reflected from the scene and intercepted by the detectorelement of detector array 154 connected to the unit cell electricalinput. The detector array 154 may be an array of avalanche photodiodes,capable of photoelectron amplification, and modulated by an incidentlight signal at the design wavelength. The detector array 154 elementsmay also be a P-intrinsic-N design or N-intrinsic-P design with thedominant carrier being holes or electrons respectively; in which casethe corresponding ROIC 156 would have the polarity of the bias voltagesand amplifier inputs adjusted accordingly. The hybrid assembly ofdetector array 154 and readout integrated circuit 156 of the preferredembodiment is shown in FIG. 20, and the assembly is then mounted to asupporting circuit assembly, typically on a FR-4 substrate or ceramicsubstrate (not shown). The circuit assembly provides support circuitrywhich supplies conditioned power, a reference clock signal, calibrationconstants, and selection inputs for the readout column and row, amongother support functions, while receiving and registering range andintensity outputs from the readout integrated circuit 156 for theindividual elements of the detector array 154, and shown here in FIG.18. Many of these support functions may be implemented in RISCprocessors which reside on the same circuit assembly. A detector biasconverter circuit 166 applies a time varying detector bias to thedetector array 154 which provides optimum detector bias levels to reducethe hazards of saturation in the near field of view of detector array154, while maximizing the potential for detection of distant objects inthe field of view of detector array 154. The contour of the time varyingdetector bias supplied by detector bias converter 166 is formulated bycontrol processor 136 based on inputs from the data reduction processor164, indicating the reflectivity and distance of objects or points inthe scene in the field of view of the detector array 154. Controlprocessor 136 also provides several clock and timing signals from atiming core 140 to readout integrated circuit 156, data reductionprocessor 164, analog-to-digital converters 160, object trackingprocessor 182, and their associated memories. Control processor 136relies on a temperature stabilized frequency reference 168 to generate avariety of clocks and timing signals. Temperature stabilized frequencyreference 168 may be a temperature compensated crystal oscillator(TCXO), dielectric resonator oscillator (DRO), or surface acoustic wavedevice (SAW). Timing core 140 resident on control processor 136 mayinclude a high frequency tunable oscillator, programmable prescalerdividers, phase comparators, and error amplifiers.

Continuing with FIG. 18, control processor 136, data reduction processor164, and object tracking processor 182 each have an associated memoryfor storing programs, data, constants, and the results of operations andcalculations. These memories, each associated with a companion digitalprocessor, may include ROM, EPROM, or other non-volatile memory such asflash. They may also include a volatile memory such as SRAM or DRAM, andboth volatile and non volatile memory may be integrated into each of therespective processors. A common frame memory 176 serves to hold a numberof frames, each frame being the image resulting from a single laserpulse. Both data reduction processor 164 and object tracking processor182 may perform 3D image processing, to reduce the load on a centralprocessing unit normally associated with ladar system controller 104.There are two modes of data collection, the first being SULAR, or aprogressive scan in depth. Each laser pulse typically results in 20“slices” of data, similar to a CAT scan, and each “slice” may be storedas a single page in the common frame memory 176. With each pixelsampling at a 2 nanosecond interval, the “slices” are each a layer ofthe image space at roughly 1 foot differences in depth. The 20 slicesrepresent a frame of data, and the sampling for a succeeding laser pulsemay be started at 20 feet further in depth, so that the entire imagespace up to 1000 feet in range or depth, may be swept out in asuccession of 50 laser illuminating pulses, each laser pulse responseconsisting of 20 “slices” of data held in a single frame entry. In somecases, the frame memory may be large enough to hold all 50 frames ofdata. The reduction of the data might then take place in an externalcomputer, as in the case of data taken to map an underwater surface, ora forest with tree cover, or any static landscape, where sophisticatedpost-processing techniques in software may yield superior accuracy orresolution. A second data acquisition mode is the TRIGGER mode, wherethe individual pixels each look for a pulse response, and upon a certainpulse threshold criteria being met, the 20 analog samples bracketing thepulse time of arrival are retained in the pixel analog memories, and arunning digital counter is frozen with a nominal range measurement. The20 analog samples are output from each pixel through the “A” and “B”outputs 158 of readout integrated circuit 156, which represent theinterleaved row or column values of the 128×128 pixel of the presentdesign. The “A” and “B” outputs are analog outputs, and the analogsamples presented there are converted to digital values by the dualchannel analog-to-digital (A/D) converter 160. Interleaving the outputsmeans one of the outputs (“A”) reads out the odd numbered lines of thereadout IC 156, and the other output (“B”) reads out the even numberedlines of the readout IC 156. The digital outputs 162 of the A/Dconverters 160 connect to the inputs of the data reduction processor164. A/D converters 160 may also be integrated into readout integratedcircuit 156. The digital outputs 162 are typically 10 or 12 bit digitalrepresentations of the uncorrected analog samples measured at each pixelof the readout IC 156, but other representations with greater or fewerbits may be used, depending on the application. The rate of the digitaloutputs 162 depends upon the frame rate and number of pixels in thearray. In TRIGGER mode, a great deal of data reduction has alreadytranspired, since the entire range or depth space may be swept out inthe timeframe of a single laser pulse, and the data reduction processor164 would only operate on the 20 analog samples stored in each unit cellin order to refine the nominal range measurement received from eachpixel (unit cell) of the array. The data reduction processor 164 refinesthe nominal range measurements received from each pixel by curve fittingof the analog samples to the shape of the outgoing laser illuminatingpulse, which is preserved by the reference ARC pulse signal. In TRIGGERacquisition mode, the frame memory 176 only needs to hold a “pointcloud” image for each illuminating laser pulse. The term “point cloud”refers to an image created by the range and intensity of the reflectedlight pulse as detected by each pixel of the 128×128 array of thepresent design. In TRIGGER mode, the data reduction processor servesmostly to refine the range and intensity (R&I) measurements made by eachpixel prior to passing the R&I data to the frame memory 176 over databus 174, and no “slice” data or analog samples are retained in memoryindependently of the R&I “point cloud” data in this acquisition mode.Frame memory 176 provides individual or multiple frames, or full pointcloud images, to control processor 136 over data bus 172, and to anoptional object tracking processor 182 over data bus 178 as required.

As shown in FIG. 18, data reduction processor 164 and control processor136 may be of the same type, a reduced instruction set (RISC) digitalprocessor with hardware encoded integer and floating point arithmeticunits. Object tracking processor 182 may also be of the same type asRISC processors 164 and 136, but may in some cases be a processor withgreater capability, suitable for highly complex graphical processing.Object tracking processor 182 may have in addition to hardware encodedinteger and floating point arithmetic units, a number of hardwareencoded matrix arithmetic functions, including but not limited to;matrix determinant, matrix multiplication, and matrix inversion. Inoperation, the control processor 136 controls readout integrated circuit156, A/D converters 160, data reduction processor 164 and objecttracking processor 182 through a bidirectional control bus 170 whichallows for the master, control processor 136 to pass commands on apriority basis to the dependent peripheral functions; readout IC 156,A/D converters 160, data reduction processor 164, and object trackingprocessor 182. Bidirectional control bus 170 also serves to returnstatus and process parameter data to control processor 136 from readoutIC 156, A/D converters 160, data reduction processor 164, and objecttracking processor 182. Data reduction processor 164 refines the nominalrange data and adjusts each pixel intensity data developed from thedigitized analog samples received from A/D converters 160, and outputs afull image frame via unidirectional data bus 174 to frame memory 176,which is a dual port memory having the capacity of holding severalframes to several thousands of frames, depending on the application.Object tracking processor 182 has internal memory with sufficientcapacity to hold multiple frames of image data, allowing for multi-framesynthesis processes, including video compression, single frame ormulti-frame resolution enhancement, statistical processing, and objectidentification and tracking. The outputs of object tracking processor182 are transmitted through unidirectional data bus 180 to acommunications port 138, which may be resident on control processor 136.All slice data, range and intensity data, control, and communicationsthen pass between communications port 138 and a centralized ladar systemcontroller 104, (FIG. 17) through bidirectional connections 98. Powerand ground connections (not shown) may be supplied through anelectromechanical interface. Bidirectional connections 98 may beelectrical or optical transmission lines, and the electromechanicalinterface may be a DB-25 electrical connector, or a hybrid optical andelectrical connector, or a special automotive connector configured tocarry signals bidirectionally for the long range ladar sensor 94 as wellas electrical connections for a headlamp assembly which may have thelong range ladar sensor 94 embedded therein. Bidirectional connections98 may be high speed serial connections such as Ethernet, USB or FibreChannel, or may also be parallel high speed connections such asInfiniband, etc., or may be a combination of high speed serial andparallel connections, without limitation to those listed here.Bidirectional connections 98 also serve to upload information to controlprocessor 136, including program updates for data reduction processor164, object tracking processor 182, and global position reference data,as well as application specific control parameters for the remainder ofthe long range ladar sensor 94 functional blocks. Inertial and verticalreference 120 also provides data to the long range ladar sensor 94 fromthe host vehicle 2 through the vehicle electrical systems and CPU 114,bidirectional electrical connections 112, and the ladar systemcontroller 104 as needed (see FIG. 16). Likewise, any other data fromthe host vehicle 2 which may be useful to the long range ladar sensor 94may be provided in the same manner as the inertial and verticalreference data. Inertial and vertical reference data may be utilized inaddition to external position references by control processor 136, whichmay pass position and inertial reference data to data reductionprocessor 164 for adjustment of range and intensity data, and to objecttracking processor 182 for utilization in multi-frame data synthesisprocesses. The vertical reference commonly provides for measurement ofpitch and roll, and is adapted to readout an elevation angle, and atwist angle (analogous to roll) with respect to a horizontal planesurface normal to the force of gravity. The long range ladar sensor 94typically employs a q-switched solid state laser, which produces asingle output pulse with a Gaussian profile if properly controlled. Thepulse shape of a solid state laser of this type is not easily modulated,and therefore must be dealt with “as is” by the long range ladar sensor94 receiver section. The operations of a short range ladar sensor 100 ofthe type which are typically embedded in an auxiliary lamp assembly suchas a taillight, turn signal, or parking light are the same as theoperations of the long range ladar sensor 94 described above with someexceptions. The short range ladar sensor 100 of the preferred embodimentemploys a semiconductor laser which may be modulated in several ways, asopposed to the solid state laser typically employed in a long rangeladar sensor 94 of the preferred embodiment. The long range ladar sensor94 and short range ladar sensor 100 may differ only in the type of laseremployed and the type of laser modulation. The transmit optics 150 andreceive optics 152 may also differ, owing to the different fields ofview for a long range ladar sensor 94 and a short range ladar sensor100. Differences in the transmitted laser pulse modulation between thelong range ladar sensor 94 and short range ladar sensor 100 may beaccommodated by the flexible nature of the readout IC 156 samplingmodes, and the data reduction processor 164 programmability. The hostvehicle 2 may have a number of connector receptacles generally availablefor receiving mating connector plugs from USB, Ethernet, RJ-45, or otherinterface connection, and which may alternatively be used to attach longrange ladar sensors 94 or short range ladar sensors 100 of the typedescribed herein.

In the preferred embodiments described herein, a number of digitalprocessors have been identified, some associated with the host vehicle(2), some associated with the ladar subsystem (3), and some associatedwith the individual ladar sensors (3). The partitioning and the namingof these various digital processors has been made based on engineeringjudgment, but other partitioning and naming conventions may be usedwithout changing the scope or intent, or affecting the utility of theinvention. Those processors associated with the vehicle; the vehicle CPU118, and the collision processor and airbag control unit 114, may becombined in some future embodiments. A combined vehicle CPU 118 andcollision processor and airbag control unit 114 may also incorporateladar system controller 104, which is normally associated with the ladarsubsystem. The ladar system controller 104 (including scene processor128 and control processor 132) may in some alternative embodiments beeliminated as a circuit, and only the functions normally performed byladar system controller 104, as described herein as contemplated for usewith the present invention, would then be assumed by a more powerfulvehicle CPU 118. Likewise, the object tracking processor 182 of theindividual ladar sensor could be absorbed into the vehicle CPU 114, ascould other ladar sensor processors such as the data reduction processor164 and control processor 136. This would follow a trend toward greatercentralization of the computing power in the vehicle. A trend towardsdecentralization may also take place in reverse, some alternativeembodiments having ever more of the processing power pushed down intothe ladar sensor subsystem. In other alternative embodiments, perhaps ina robotic vehicle where only a single ladar sensor might be installed,substantially all of the processing power could be incorporated in theindividual ladar sensor itself. The term digital processor may be usedgenerically to describe either digital controllers or digital computers,as many controllers may also perform pure mathematical computations, orperform data reduction, and since many digital computers may alsoperform control operations. Whether a digital processor is termed acontroller or a computer is a descriptive distinction, and not meant tolimit the application or function of either device.

Continuing with FIG. 18, the use of a semiconducting laser in apreferred embodiment for a short range ladar sensor 100 allows fortailoring of the drive current to a VCSEL laser, one example of asemiconductor laser, or any diode laser, so as to produce a Gaussianoptical pulse shape with only slight deviations. The VCSEL response timeis in the sub-nanosecond regime, and the typical pulse width might be5-100 nanoseconds at the half power points. In the diagram of FIG. 18,the VCSEL and laser driver would be part of the pulsed laser transmitter146, and the desired pulse or waveshape is itself produced by adigital-to-analog converter 144 which has a typical conversion rate of200-300 MHz, so any deviations in the output pulse shape from theGaussian ideal may be compensated for in the lookup table in memory 142associated with control processor 136, which serves as the digitalreference for the drive current waveform supplied to the laser driverwithin pulsed laser transmitter 146 by the D/A converter. A Gaussiansingle pulse modulation scheme works well at short ranges, given thelimited optical power available from a VCSEL laser. Extending the rangeof a VCSEL laser transmitter may be done using more sophisticatedmodulation schemes such as multi-pulse sequences, sinewave bursts, etc.The VCSEL laser and modulation schemes as described herein withreference to short range ladar sensor 100 may be used to replace thesolid state laser in pulsed laser transmitter 146 of the long rangeladar sensor 94 to reduce cost, size, power consumption, and/or enhancereliability.

The unit cell electronics depicted in FIG. 19 is well adapted to workwith a Gaussian single pulse modulation scheme, and works advantageouslywith other modulation schemes as well, including sequences offlat-topped pulses, Gaussian, or otherwise shaped pulses. These pulsesmay be of varying width and spacing, in order to reduce rangeambiguities, and may also be random pulse sequences, or in other cases,Barker coded pulse sequences. In the typical operation of a long rangeladar sensor 94 having a solid state laser producing a single Gaussianoutput pulse, some portion of the pulsed laser light reflected from asurface in the field of view of the long range ladar sensor 94 isconcentrated and focused by receive optics 152 and falls on anindividual detector element 180 of detector array 154. The individualelement 180 is typically an avalanche photodiode, but may be a PIN orNIP, or other structure. Each individual element 180 of detector array154 is formed in a semiconducting film comprised of silicon, indiumgallium arsenide phosphide, aluminum gallium arsenide, indium galliumnitride, or other semiconducting compound appropriate to the wavelengthof operation. Each individual element 180 is biased with a voltage by abias voltage distribution network VDET 183. The reflected light signalincident upon the individual detector element 180 is converted to anelectronic signal, typically a photocurrent, and amplified by inputamplifier 182, typically a transimpedance amplifier. The output of inputamplifier 182 is distributed to a trigger circuit 170 as well as anumber of analog sampling gates 190. The trigger circuit 170 istypically a threshold voltage comparator, set to trigger when a pulse isreceived which exceeds a predetermined magnitude, though other pulsedetection schemes may be used. After a programmable delay through delaycircuit 198, the circular selector 192 is frozen by the logic transitionof trigger circuit 170 output. Prior to the detection of a receivedpulse by trigger circuit 170, the sample clock 196 causes the state ofcircular selector 192 to advance, enabling one of the sampling controloutputs S1-S3, which in turn causes a sampling of the input amplifier182 output by one of the sampling gates 190. The number of transitionsof sample clock 196 are counted by counter 194, as the circular selector192 outputs a logic transition to counter 194 for every cycle of thesampling clock after the release of the active low reset line 195.Circular selector 192 may cycle through outputs S1-S3 in order, or mayhave a different order, depending on the programming. A second circularselector 192, and sample clock 196 may operate in parallel, along withcounter 194, analog sampling gates 190 and analog memory cells 188. Thecombination of sample clock 196, counter 194, circular selector 192,sampling gates 190, and memory cells 188 may be termed a unit cellsampling structure 197, indicated by the short dashed line border. Two,three, or more of these sampling structures may be operated in parallelon the output of input amplifier 182, with the advantages of such astructure to be described later in regards to range ambiguity. Shown inFIG. 19 are three sampling gates, and analog memory cells, but thenumber may be several hundred or more on some readout ICs 156. Once allof the analog sample data has been taken, a control command from thecontrol processor 136 initiates a readout cycle by activating outputcontrol 184 and output amplifier 186 to readout the contents of theanalog memory cells 188 in a predetermined order.

In a typical short range ladar sensor 100, and assuming a 1 cm² VCSELarray with a 5 kW/cm² power density, and depending upon the reflectivityof the objects in the field of view of short range ladar sensor 100, andthe responsivity and excess noise of the detector array 154, theeffective range of a Gaussian single pulse modulation scheme might be inthe range of 10-20 meters, using a simple threshold detection technique.Without resorting to a large VCSEL array, which might be expensive andmight require a large discharge capacitor to supply a large currentpulse, more sophisticated modulation and detection techniques can beused to create additional processing gains, to effectively increase thesignal-to-noise ratio, and thus extend the range of the short rangeladar sensor 100 without requiring an increase in power. In a firstmodulation scheme, which produces a Gaussian single pulse modulation, adetection technique may be employed which uses the digitized analogsamples from each unit cell electrical circuit, and processes thesesamples in a digital matched filter to find the centroid of the receivedpulse, resulting in significant processing gain. The processing gainsresulting from this structure are proportional to the square root of thenumber of samples used in the filtering algorithm. For example, a unitcell electrical circuit with 256 analog memory cells 188 could yield aprocessing gain of 16 if all the available analog samples were used in amatched filter algorithm, assuming Gaussian single pulse modulation, anda normal noise distribution. The term “processing gain” is used here todescribe the increase in effective signal-to-noise ratio (SNR) realizedby performing the described operations on the voltage samples. Assumingthe pulsed laser light is distributed uniformly over just the field ofview of the receive optics 152, the effective range of the ladar alsoincreases as the square root of the transmitted power (or SNR), and anincrease in range to 40-80 meters could be the result. Single pulseGaussian modulation may be characteristic of either a solid state laseror a semiconductor laser with a simple driver, and thus may be anattribute of either a long range ladar sensor 94 or a short range ladarsensor 100.

In a second modulation scheme, a VCSEL array modulated with a series ofBarker encoded flat-topped or Gaussian pulses can be sampled by the unitcell electronics of FIG. 19 and analyzed by data reduction processor 164for range and intensity estimates. In a third modulation scheme, a VCSELarray modulated with a pulsed sinewave allows for greater cumulativeenergy to be reflected from a feature in a scene in the field of view ofeither a short range ladar sensor 100 or a long range ladar sensor 94without an increase in peak power. Each peak of a pulsed sinewave willhave a separate reflection from an object or feature in the scene in thefield of view of the ladar sensor (94, 100) and the unit cell electricalcircuit of FIG. 19 allows the ladar sensor receiver to respond to thecumulative energy from many of these reflected pulses using a minimum ofcircuitry. The waveform in a preferred embodiment is a number ofsinewave cycles, and the number could be quite large, depending on anumber of factors. The receiver circuitry of the unit cell electronicsshown in FIG. 19 is capable of sampling or of synchronously detectingthe cumulative energy of the returned pulse peaks. Two sampling modesmay be supported by the unit cell sampling structure shown in FIG. 19.When taking analog samples of single pulse or multi pulse sequences,wherein analog samples of an incoming waveform are being sequentiallytaken, the sampling impedance control 193 (Z) to the circular selector192 would be set to a minimum value. The sampling frequency of sampleclock 196 would also be selected to produce 10 or perhaps 20, analogsamples during each pulse width. When the sampling impedance control 193is set to a minimum, the sample controls S1, S2, S3 . . . turn on withfull voltage during a sampling cycle. Since each sampling gate 190 is afield effect transistor, increasing the sample control voltage S1-S3will increase the gate-source voltage on the sampling FET, thus loweringthe impedance of the channel between source and drain, and setting thesampling gate impedance to a minimum. When the sampling gate 190impedance is set to a minimum, the storage capacitor serving as analogmemory cell 188 charges rapidly to the voltage present at the output ofinput amplifier 182. This mode can be termed “instantaneous voltagesampling” to distinguish the mode from a second sampling mode, which isselected when the sampling impedance control 193 is set to a higher, oreven maximum value. When the sampling impedance control 193 is selectedfor high impedance, or maximum series resistance value, the outputsS1-S3 would be at or near minimum voltages when enabled, resulting in alower gate-source voltage across each of the sampling gate FETs 190, andthus a higher sampling gate series resistance in the channel betweensource and drain of each sampling gate 190 FET. With the seriesresistance of the sampling gates 190 set to high or maximum value, theeffect is to cause an R-C filter to develop, with the analog memory cell188 storage capacitor performing as an integrating capacitor. Thissecond sampling mode may be very useful when a sinusoidal modulation isapplied to the pulsed laser transmitter 146 in the case where the laseris a semiconductor laser, typically a high efficiency VCSEL. By applyinga sampling clock to the sampling gate 190 driven by S1, and which is thesame frequency as the sinusoidal modulation, a sum frequency and adifference frequency will be in the sampled signal, and the analogmemory cell 188 storage capacitor will filter out the sum frequency, andthe difference frequency will be zero, leaving only a DC voltagecomponent, which will be a trigonometric function of the phasedifference. Over a number of cycles of the sinusoidal modulation fromthe output of input amplifier 182, this DC voltage will emerge as thesine or cosine of the phase difference. This phase difference isproportional to the range to a reflecting surface. To improve theprocessing gain, the second sampling gate driven by the S2 signal isdriven by the same sampling clock frequency, but shifted by 90 degreesin phase, and the greater of the two DC voltages, or a ratio of the twovoltages, may used to estimate phase, and thereby range. Typically, aratio is preferred, as it removes the variation in amplitude of theincoming sinewave as an error term. This type of detection relies on“In-phase” and “Quadrature-phase” local references, and is oftenreferred to as an “I&Q” detection scheme. Thus, the sampling gates 190can be operated as instantaneous voltage samplers in a first samplingmode, or as frequency mixers in a second sampling mode, depending on thestate of the sampling impedance control 193, and the frequency appliedby sampling clock 196. In the first sampling mode, the shape of a pulseor sequence of pulses may be acquired, and in second sampling mode, aperiodic waveform modulation such as a sinewave, may be demodulatedthrough the frequency mixing effect and integration on a storagecapacitor, resulting in a phase measurement and thereby range. In athird modulation case, two and perhaps three sinewaves of differentfrequencies are superimposed as a modulation signal on a semiconductorlaser, and the received waveform output from input amplifier 182 issampled by 2 or 3 unit cell sampling structures 197 arranged inparallel, and operating at the 2 or 3 different frequencies of themodulation signal. Each frequency is demodulated and the phase measuredby the unit cell sampling structure tuned to the frequency of interestby feeding the appropriate sampling frequency from sample clock 196,typically a copy of the modulation frequency.

When measuring the phase of reflected laser energy with respect to atransmitted laser sinewave modulation, certain limits must be observed.If the ladar should have a maximum range capability of 150 meters infree space, the total round trip delay from transmit to receive would bearound 1 microsecond. For the phase measurement to be meaningful, thefrequency of transmission must therefore be less than 1 MHz to avoidspatial (distance) aliasing of targets at the 150 meter limit. In otherwords, the further the target, the lower the frequency of modulationmust be for a single modulation frequency phase measurement to bemeaningful. In a conventional sweep radar, the dwell time on the targetis limited, so return signals beyond the maximum design range often donot appear as aliased, or “ghost” signals at a shorter apparent range.In the ladar of the instant invention, the typical mode is a staringmode, and there is no sweep of the illuminating beam or receivingantenna across the target space. Therefore, in the ladar sensor (94,100)of the present design, responses from targets beyond the designedmaximum range could produce an aliased response (one in which the phaseshift is greater than 2π). A method for resolving these aliased, or“ghost” images is to illuminate the target in a second or thirdtransmission with a slightly different frequency; for example 0.99 MHzversus the 1.0 MHz in a first gated sinewave illuminating pulse. If thetarget image remains at the same apparent range, it is likely a realtarget at a range less than the design maximum range limit. If theapparent range of the target shifts at the second illuminatingfrequency, it is likely the image is an aliased, or “ghost” image from atarget at a distance beyond the design maximum range of the ladar sensor(94, 100). The ladar sensor (94, 100) of the instant invention makes useof a frequency agile transmitter which can rapidly tune from a firsttransmission frequency to a second transmission frequency, and more ifnecessary. In a preferred embodiment, the unit cell sampling structure197 is doubled or tripled, and operated in parallel, and two or threesinewave modulation signals are superimposed on the semiconductor lasertransmitter. When using multiple frequency modulation, the individualfrequencies should not be simple harmonics of each other; i.e., theyshould not be related by fractions of low value integers. The ladarsensor (94, 100) in a preferred embodiment makes use of a semiconductorVCSEL laser, enabling the use of shaped single pulses, shaped multiplepulses, shaped and encoded multiple pulses, gated sinewave, gatedchirped sinewave, and multi-frequency gated sinewave modulation schemes.In alternative embodiments, a low power semiconductor laser may beelectronically modulated, and the resulting modulated optical outputamplified by an optical amplifier. By selecting a modulation regimeappropriate to the particular scene or objects to be imaged, theflexible modulation capabilities of the present design result in aminimum sized pulsed laser illuminating source with maximum performancein range and resolution.

FIG. 20 is a diagram showing the mating of detector array 154 withreadout IC 156. Row amplifiers 206 and column amplifiers 204 allow theoutput from a unit cell electrical circuit 208 to be output as part of arow output or column output read cycle. All signals to and from readoutIC 156 are communicated through bond pads 202 at the periphery of theROIC 156. Atop each unit cell electrical circuit 208 is an indium bump210 which is compressed and deformed under temperature and pressure aspart of the bonding process which mates detector array 154 to readout IC156. The indium bump 210 may instead be a low temperature solder bump,which may be reflowed to permanently bond detector array 154 to readoutIC 156. The arrow shows the direction of mating, and the top of detectorarray 154 shows the grid pattern of an optional microlens arraycomprised of lens elements 200 which collect and focus light into eachof the individual detector elements of detector array 154 formed on theanterior surface.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. An impact mitigation system comprising: a vehiclewith a ladar sensor mounted thereto, an impact mitigation device, saidimpact mitigation device mounted to said vehicle, an impact control unitoperably connected to activate said impact mitigation device, and saidladar sensor comprising; a receiving lens assembly, a laser transmitterwith a modulated laser light output and a diffusing optic forilluminating a scene in a field of view of said ladar sensor, a twodimensional array of light sensitive detectors positioned at a focalplane of said receiving lens assembly, each of said light sensitivedetectors with an output producing an electrical response signal from areflected portion of said modulated laser light output, a readoutintegrated circuit with a plurality of unit cell electrical circuits,each of said unit cell electrical circuits having an input connected toone of the light sensitive detector outputs, each unit cell electricalcircuit having an electrical response signal demodulator and a rangemeasuring circuit connected to an output of said electrical responsesignal demodulator, the range measuring circuit further connected to areference signal providing a zero range reference for the rangemeasuring circuit, a detector bias circuit connected to at least onevoltage distribution grid of said array of light sensitive detectors, adigital processor connected to receive an output from the rangemeasuring circuit and provide an input for the impact control unit, anda temperature stabilized frequency reference connected through thedigital processor to provide clocking signals.
 2. The impact mitigationsystem of claim 1 further comprising a duplex radio link connected tothe digital processor for interconnecting with a second digitalprocessor in a second vehicle.
 3. The impact mitigation system of claim1 wherein said impact mitigation device is an airbag.
 4. The impactmitigation system of claim 1 wherein said impact mitigation deviceincorporates a hydraulic actuator.
 5. The impact mitigation system ofclaim 1 wherein said laser transmitter comprises a vertical cavitysurface emitting laser formed in a semiconducting gain medium with atleast one element selected from the set of indium, gallium, arsenic,phosphorus.
 6. The impact mitigation system of claim 1 wherein saidmodulated laser light output is modulated with a waveform selected fromthe set of a single Gaussian pulse profile, multiple Gaussian profilepulses, a single flat-topped pulse profile, multiple flat-topped pulses,a pulsed sinewave, and a chirped sinewave pulse.
 7. The impactmitigation system of claim 1 wherein said laser transmitter comprises anoptically pumped solid state laser formed in a gain medium selected fromthe set of yttrium aluminum garnet, erbium doped glass, neodymium dopedyttrium aluminum garnet, and erbium doped yttrium aluminum garnet. 8.The impact mitigation system of claim 1 wherein said two dimensionalarray of light sensitive detectors is mounted directly to said readoutintegrated circuit.
 9. The impact mitigation system of claim 1 whereinsaid ladar sensor is integrated into a headlight assembly.
 10. Theimpact mitigation system of claim 1 wherein said ladar sensor isintegrated into an auxiliary lamp assembly selected from the set of aturn signal, taillight, parking light, mirror assembly, and brake light.11. The impact mitigation system of claim 1 wherein said vehicle furtherhas at least one two dimensional imaging camera sighted to have a fieldof view overlapping the field of view of said ladar sensor, and saidvehicle further having a digital processor adapted to merge the datafrom said ladar sensor with data from the two dimensional imagingcamera.
 12. An active vehicle suspension system comprising: a vehiclewith a ladar sensor mounted thereto, a suspension actuator, thesuspension actuator attached to a suspension member of at least onewheel of said vehicle, and the suspension actuator also attached to achassis of said vehicle, and the suspension actuator adapted to activelyraise or lower said wheel in response to a control input, a suspensioncontrol processor providing said control input, and said ladar sensorcomprising; a receiving lens assembly, a laser transmitter and saidlaser transmitter with a modulated laser light output and a diffusingoptic for illuminating a scene in the field of view of said ladarsensor, a two dimensional array of light sensitive detectors positionedat a focal plane of said receiving lens assembly, each of said lightsensitive detectors with an output producing an electrical responsesignal from a reflected portion of said modulated laser light output, areadout integrated circuit with a plurality of unit cell electricalcircuits, each of said unit cell electrical circuits having an inputconnected to one of said light sensitive detector outputs, each unitcell electrical circuit having an electrical response signal demodulatorand a range measuring circuit connected to an output of the electricalresponse signal demodulator, the range measuring circuit furtherconnected to a reference signal providing a zero range reference for therange measuring circuit, and a detector bias circuit connected to atleast one voltage distribution grid of said array of light sensitivedetectors, a digital processor connected to receive an output from therange measuring circuit and provide an input for the suspension controlprocessor, and a temperature stabilized frequency reference connected tothe digital processor.
 13. The system of claim 12 wherein said lasertransmitter comprises a semiconductor laser formed in a semiconductinggain medium with at least one element selected from the set of indium,gallium, arsenic, phosphorus.
 14. The system of claim 12 wherein saidmodulated laser light output is modulated with a waveform selected fromthe set of a single Gaussian pulse profile, multiple Gaussian profilepulses, a single flat-topped pulse profile, multiple flat-topped pulses,a pulsed sinewave, and a chirped sinewave pulse.
 15. The system of claim12 wherein said laser transmitter comprises an optically pumped solidstate laser formed in a gain medium selected from the set of yttriumaluminum garnet, erbium doped glass, neodymium doped yttrium aluminumgarnet, and erbium doped yttrium aluminum garnet.
 16. The system ofclaim 12 wherein said two dimensional array of light sensitive detectorsis mounted directly to said readout integrated circuit.
 17. The systemof claim 12 wherein said control input is selected from the set of a gaspressure, a hydraulic pressure, an electrical current, and an electricalvoltage.
 18. The system of claim 12 wherein said two dimensional arrayof light sensitive detectors is formed in a semiconducting film havingan element selected from the set of silicon, indium, gallium, arsenic,phosphorus, aluminum, boron, antimony, magnesium, germanium, andnitrogen.
 19. The system of claim 12 wherein said ladar sensor isintegrated into a headlight assembly.
 20. The system of claim 12 whereinsaid ladar sensor is integrated into an auxiliary lamp assembly selectedfrom the set of a turn signal, taillight, parking light, and brakelight.
 21. The system of claim 12 wherein said vehicle further has atleast one two dimensional imaging camera sighted to have a field of viewoverlapping the field of view of said ladar sensor, and said vehiclefurther having a digital processor adapted to merge the data from saidladar sensor with data from the two dimensional imaging camera.